docs: def export_output(dskey, calc_id, datadir, target_dir, export_types):
      """
      Simple UI wrapper around
      :func:`openquake.engine.export.core.export_from_db` yielding
      a summary of files exported, if any.
      """
      outkey = get_outkey(dskey, export_types.split(','))
      if export_types and not outkey:
          yield 'There is no exporter for %s, %s' % (dskey, export_types)
          return
      yield from export_from_db(outkey, calc_id, datadir, target_dir)